The effect of retained intramedullary nails on tibial bone mineral density.

BACKGROUND: Intramedullary nailing has become a standard treatment for adult tibial shaft fractures. Retained intramedullary nails have been associated with stress shielding, although their long-term effect on decreasing tibial bone mineral density is currently unclear. The purpose of this study was to determine if retained tibial intramedullary nails decrease tibial mineral density in patients with successfully treated fractures. METHODS: Patients treated with statically locked intramedullary nails for isolated, unilateral tibia shaft fractures were studied. Inclusion required that fracture had healed radiographically and that the patient returned to the pre-injury activity level. Data on patient demographic, fracture type, surgical technique, implant, and post-operative functional status were tabulated. Dual energy X-ray absorptiometry was used to measure bone mineral density in selected regions of the affected tibia and the contralateral intact tibia. Image reconstruction software was employed to ensure symmetry of the studied regions. FINDINGS: Twenty patients (mean age 43; range 22-77 years) were studied at a mean of 29 months (range 5-60 months) following intramedullary nailing. There was statistically significant reduction of mean bone mineral density in tibiae with retained intramedullary nails (1.02 g/cm(2) versus 1.06 g/cm(2); P=0.04). A significantly greater decrease in bone mineral density was detected in the reamed versus non-reamed tibiae (-7% versus +6%, respectively; P<0.05). INTERPRETATION: The present study demonstrates a small, but statistically significant overall bone mineral density decrease in healed tibiae with retained nails. Intramedullary reaming appears to be a factor potentiating the reduction of tibia bone mineral density in long-term nail retention.

The use of a virtual three-dimensional model to evaluate the intraosseous space available for percutaneous screw fixation of acetabular fractures.

We created virtual three-dimensional reconstruction models from computed tomography scans obtained from patients with acetabular fractures. Virtual cylindrical implants were placed intraosseously in the anterior column, the posterior column and across the dome of the acetabulum. The maximum diameter which was entirely contained within the bone was determined for each position of the screw. In the same model, the cross-sectional diameters of the columns were measured and compared to the maximum diameter of the corresponding virtual implant. We found that the mean maximum diameter of virtual implant accommodated by the anterior columns was 6.4 mm and that the smallest diameter of the columns was larger than the maximum diameter of the equivalent virtual implant. This study suggests that the size of the screw used for percutaneous fixation of acetabular fractures should not be based solely on the measurement of cross-sectional diameter and that virtual three-dimensional reconstructions might be useful in pre-operative planning.

In vitro pharmacokinetics of antibiotic release from locally implantable materials.

Local deposition of antibiotics has became increasingly popular in the management of open fractures or osteomyelitis, and several substances have been employed as the vehicle for delivery. Although the elution characteristics of some substances have been documented, a comparative study of the characteristics of the commonly used substances could establish the clinical indications for particular vehicles. Cylindrical pellets of uniform size (6 x 4 mm) were prepared from bone graft (BG), demineralized bone matrix (DBM), plaster of Paris (POP), or polymethylmethacrylate (PMMA), with 25 mg of tobramycin/g of substance in each pellet. The pellets were suspended in phosphate buffered saline, and the antibiotic concentration in the buffer was determined at various time intervals by an enzyme immunoassay. BG and DBM eluted 70 and 45% of their antibiotic load by 24 h, and negligible amounts were detected at 1 week; POP released 17% of its load by 24 h, with trace amounts detected at 3 weeks; and PMMA eluted 7% at 24 h, with trace amounts detected for as long as 14 days. These findings suggest that the optimal vehicle for local deposition of antibiotic depends on the clinical setting. BG and DBM may be best employed when brief antibiotic coverage is required (as for acute contaminated open fractures), whereas POP and PMMA may be better suited for long-term coverage (such as for established osteomyelitis).

Strength reduction and the effects of treatment of long bones with diaphyseal defects involving 50% of the cortex.

Currently, three criteria are accepted as indications for prophylactic internal fixation of metastatic disease in long bone, including lesions (a) destroying 50% or more of the cortex; (b) 2.5 cm or greater in diameter; or (c) with pain unrelieved by radiation therapy. Using an oblong defect configuration in which one half of the cross-sectional area was destroyed, canine femora were torsion-tested at high speed to determine (a) the actual strength reduction incurred by a lesion destroying 50% of the cortical circumference, and (b) the effects and benefits of internal fixation using polymethylmethacrylate and/or a six-hole compression plate on such a defect. The femurs with a 50% circumferential cortical defect demonstrated only 12.7 +/- 3.8% of intact strength. Defects treated with a combination of plating (all screws bicortical) and polymethylmethacrylate (torque to failure 4.39 +/- 0.90 times greater than the defect alone or TE/TD = 4.39 +/- 0.90) were statistically stronger than defects treated with polymethylmethacrylate alone (TE/TD = 2.48 +/- 0.66; p less than 0.025) or by plating alone (TE/TD = 2.61 +/- 0.91; p less than 0.025), but torque-to-failure was only increased to approximately 56% of an intact bone. Plated intact bones (TE/TD = 5.33 +/- 0.41) were significantly weaker than intact bones (TE/TD = 8.50 +/- 2.52; p less than 0.001). Our results substantiate the need for using polymethylmethacrylate and internal fixation in combination when prophylactically fixing pathologic lesions of this proportion.

Effect of ciprofloxacin on the proliferation of osteoblast-like MG-63 human osteosarcoma cells in vitro.

Locally applied antibiotic therapy is gaining popularity for the treatment of infections associated with open fractures and posttraumatic osteomyelitis. With use of local techniques, ciprofloxacin levels as high as 1,300 microg/ml, or over 200 times the bone levels achieved with intravenous administration, have been reported. To study the possible effects of ciprofloxacin on bone, osteoblast-like cells from the MG-63 human osteosarcoma cell line were studied. The cells were grown in antibiotic-free media and exposed to concentrations of ciprofloxacin at 0, 10, 100, 200, and 1,000 microg/ml to establish an initial dose-response curve. Media containing the appropriate dose of ciprofloxacin were changed every 24 hours. Cell number and [3H]thymidine incorporation per cell were determined at 0, 24, and 72 hours. A second dose-response curve was performed at concentrations of 0, 10, 20, 40, and 80 microg/ml. Three experiments, each with four observations, were performed. The results of this study demonstrated that ciprofloxacin caused significant decreases (p < 0.05) in cell number at 40 microg/ml at 24 hours and 20 microg/ml at 72 hours. [3H]thymidine incorporation per cell decreased significantly at levels of 80 microg/ml at 24 hours and 20 microg/ml at 72 hours. The authors conclude that reported local levels of ciprofloxacin seen in vivo inhibit the proliferation of human osteoblast-like cells in vitro.

Refracture of bones of the forearm after the removal of compression plates.

Of thirty-seven patients who had sixty-two diaphyseal plates removed from the forearm after fixation of a fracture, seven patients had a refracture, two of whom refractured both bones of the forearm. Six of the seven refractures were in patients who initially had had a fracture of both bones, and all were in patients in whom the original fracture had been caused by major trauma. The interval from the time of removal of the plate to refracture ranged from forty-two to 121 days. Only one of the seven patients who had a refracture had had adequate compression of the original fracture. The average interval from the time of the original trauma to internal fixation was two days in six patients who had a refracture and who originally had had primary plating, compared with 8.5 days in the patients who did not have a refracture. One of the seven patients who had a refracture had originally had delayed plating after closed treatment had failed. In retrospect, radiolucency at the site of the original fracture was seen in most patients when the plate was removed.

The fixateur interne in the reduction and stabilization of thoracolumbar spine fractures in patients with neurologic deficit.

A prospective analysis of 80 consecutive patients who underwent stabilization with the fixateur interne for thoracolumbar spine fractures with complete or incomplete paraplegia was undertaken to determine the results after bone healing. Follow-up examination at an average of 35 months (minimum, 24 months) included all 76 patients still alive. One patient died from a pulmonary embolism, and there were three other unrelated deaths. The mean wedge angle of the fractured vertebra was corrected from 17.4 degrees to 7.9 degrees and remained almost unchanged after 1 year (8.4 degrees) and 2 years, or 1 year after implant removal (8.2 degrees). Also, the wedge index showed nearly no bony loss of correction within the reduced fracture vertebra (0.61 before operation, 0.83 after operation; 0.81 at 1-year follow-up, 0.81 at 2-year follow-up, respectively). In the kyphosis angle measured by the Cobb method, however, there was a loss of 5 degrees after implant removal within the next year because of the disc space collapsed above the fractured vertebra. In this series, 70% of the cases had no formal fusion. All 29 cases of translational displacement of 4-36 mm were anatomically reduced. No neurologic or vascular complication occurred. Posterolateral fusion or transpedicular interbody fusion in the disrupted disc space is recommended.

Ureteral injury after anterior lumbar interbody fusion. A case report.

STUDY DESIGN: This case report presents a patient with ureter injury after anterior spinal fusion and its management. OBJECTIVES: To present possible causes, symptoms, diagnostic approach, and management of this rare complication. SUMMARY OF BACKGROUND DATA: The reported complications of anterior surgical approaches to the lumber spine have been predominantly vascular or neurologic. The susceptibility of the ureter to injury is emphasized by the description of an as-yet-unreported case of ureter laceration after anterior lumbar fusion. METHODS: Ureter injury was diagnosed using computed axial tomography, ultrasonography-guided aspiration, and chemical analysis of the aspirate after anterior spinal fusion. RESULTS: Early diagnosis of this injury prompted a ureter stent placement and prevented additional deterioration of renal function and infection. CONCLUSIONS: The ureter is prone to injury if not identified and protected when sharp and pointed instruments are used for retraction. Abdominal mass, low-grade fever, and leukocytosis should prompt use of computed tomography or ultrasonography-guided aspiration.

Residual intersegmental spinal mobility following limited pedicle fixation of thoracolumbar spine fractures with the fixateur interne.

The Fixateur Interne has been proposed for limited pedicle fixation of thoracolumbar spine fractures with the assumption that motion in the nontraumatized spinal segments could be maintained. To date, no data exist that both localize and quantitate spinal mobility about the fractured vertebra. Voluntary maximum lateral flexion and extension radiographs were obtained on patients with unstable thoracolumbar spine fractures at a minimum of 2 years after Fixateur Interne instrumentation (implant was removed after 1 year). Residual intersegmental motion was measured at levels adjacent to both the vertebra fracture and the fixation. Fifty-nine patients were reviewed, and the posterior vertebral body angle demonstrated a mean total sagittal motion of 2.98 degrees. Cephalad and caudal to the fractured vertebra, a mean of 1.34 degrees and 3.08 degrees, respectively, of residual motion was noted; cephalad and caudal to the previously instrumented segment a mean of 3.22 degrees and 6.88 degrees, respectively, was measured. The authors conclude that residual mobility is most evident at the caudal end of the instrumented segment, removed from the fractured vertebra. The level with end plate disruption becomes essentially ankylosed, with or without a fusion.

Segmental variations of bone mineral density in the cervical spine.

STUDY DESIGN: This study assessed the variability of segmental bone mineral density in the lower cervical spine (C4 through C7). A mean segmental bone mineral density value at each level was determined for all specimens, and a mean coefficient of variation among the 17 specimens was calculated. OBJECTIVES: To quantify the degree of intersegmental bone mineral density variations within cadaveric lower cervical spine segments. SUMMARY OF BACKGROUND DATA: Bone mineral density studies in the thoracic and lumbar spine have shown a high degree of variability between spinal segments; however, the extent of segmental bone mineral density variability in the cervical spine is unknown. METHODS: Seventeen human cadaveric cervical spine specimens (C4 through C7) were scanned in a water bath using dual energy x-ray absorptiometry in a lateral direction. Segmental bone mineral density of the vertebral bodies of all specimens were analyzed with respect to differences between segments within each specimen. RESULTS: The mean coefficient of segmental bone mineral density variations within each specimen for all spines was 14.8% (range, 5.8%-22.9%). Bone mineral density mean values and ranges at each level were as follows: C4, 0.720 g/cm2 (range, 0.367-1.161 g/cm2); C5, 0.784 g/cm2 (range, 0.348-1.268 g/cm2); C6, 0.735 g/cm2 (range 0.367-1.450 g/cm2); C7, 0.590 g/cm2 (range, 0.340-1.040 g/cm2). Paired analysis of difference between all levels for 16 specimens demonstrated the bone mineral density at the C7 level to be significantly lower than at all other levels (P < 0.05). CONCLUSION: Our data show that significant interlevel bone mineral density variability exists in the lower cervical spine, and suggests that random single segment bone mineral density sampling or mean specimen bone mineral density values may not be relevant.

Bending of the Cotrel-Dubousset instrumentation after direct trauma: a case report.

STUDY DESIGN: Case report. OBJECTIVES: To describe a fracture through the fusion mass of a spine that had been corrected previously with Cotrel-Dubousset rods. These rods had failed in bending after direct trauma. SUMMARY OF BACKGROUND DATA: Nine years after successful treatment of scoliosis with Cotrel-Dubousset instrumentation, the patient was in a motor vehicle accident and sustained a hyperextension spine injury with complete L1-L2 paraplegia and disruption of the fusion mass. The Cotrel-Dubousset instrumentation rods, which failed in bending, could not be corrected in situ, and the angulated segments had to be resected. The spine then became extremely unstable, and the patient consulted the authors for definitive stabilization. RESULTS: The spine was stabilized by attaching the proximal and distal retained Cotrel-Dubousset instrumentation to supplemental rods in a "domino" fashion. Crosslinks were added to improve the torsional stability. Intraoperatively, the fracture was well reduced, and the fixation was stable. A posterolateral fusion was performed with allogenic bone graft. CONCLUSION: Bent Cotrel-Dubousset instrumentation rods are still very strong and may not correct in situ.- If resection is required, the retained portions of Cotrel-Dubousset instrumentation can serve as attachments to restore stable fixation a "domino"technique.

Duration of symptoms and disc configuration in chemonucleolysis.

Previous studies have compared the effectiveness of chemonucleolysis with surgery, but currently, no objective criteria have been correlated with the clinical outcome. The authors reviewed 28 cases where the patients had undergone chymopapain injection to determine the significance of disc herniation size, disc space height reduction, and the duration of symptoms on clinical outcome. All patients had a complete history, physical examination, and discogram, and most had pre- and post-injection computerized tomography (CT) or myelogram. Nine of the 28 patients were considered clinical failures. Seven underwent laminectomy and discectomy and were improved markedly. Two patients were advised to have surgery but refused and were considered clinical failures. The causes of failure were unknown in three patients, free fragment in two patients, and diabetic neuropathy in one. Only two patients who did well showed complete resolution of the disc deformity on repeat CT scan. The remainder still had evidence of an avascular deformity that persisted although reduced in size. The failures showed no changes in disc size. The height of the disc space was too variable to be correlated with clinical outcome. Patients who failed had a longer duration of symptoms than the ones who did well (15.1 months for failures vs. 5 months). Therefore, some reduction of disc deformity size, but not necessarily complete reduction, is necessary for a good result, and the enzyme is not as effective in patients with long-standing symptoms.

Esophageal perforation following anterior cervical spine surgery.

The authors surveyed the Cervical Spine Research Society to compile a series of esophageal perforations following anterior cervical spine surgery. Twenty-two cases were assembled. Six occurred at the time of surgery, 6 in the postoperative period, and 10 weeks to months later. Eight surgeries were because of fracture. Hardware was implicated in 25% of cases occurring after surgery. Diagnosis was confirmed most often by direct vision at reexploration or esophography. Treatment usually consisted of drainage, repair, and parenteral antibiotics; 2 cases were successfully treated by enteral feeding and antibiotics alone. There was one fatality, and all patients required prolonged hospitalization. Cervical fracture and the use of hardware may be associated with this complication. Clinical suspicion and esophography are important diagnostic tools. Drainage and parenteral antibiotics are recommended treatment.

Imaging assessment of sacroiliac screw placement relative to the neuroforamen.

STUDY DESIGN: Twenty-four cannulated sacroiliac screws were placed bilaterally into 12 cadaveric pelvi (12 titanium screws and 12 stainless-steel screws) and were imaged using conventional and multiplanar reconstructed computed tomography. OBJECTIVES: To determine whether sacroiliac screw position assessment relative to the neuroforamen is enhanced by: 1) computed tomography using multiplanar reconstructions and 2) the use of titanium screws rather than stainless-steel screws. SUMMARY OF BACKGROUND DATA: To the authors' knowledge, there have been no prior studies demonstrating the accuracy of multiplanar computed tomography compared with that of conventional (axial) tomography in determining the position of sacroiliac screws relative to the neuroforamen. Although titanium screws have been shown to have less scatter than stainless-steel screws, the effect of alloy composition on the radiographic accuracy of interpreting the screw position relative to the sacral neuroforamen is unknown. METHODS: Screws were deliberately placed into: position A, in which the screw did not violate the neuroforamen; position B, in which the threads of the screw came within 3 mm of the neuroforamen; and position C, in which the screw clearly was nearly centered in the neuroforamen. The degrees of accuracy in assessing screw position relative to the neuroforamen using conventional (axial) images and using multiplanar reconstructed images were compared. RESULTS: The axial images were accurate in determining screw position relative to the neuroforamen in 50% of cases in which titanium screws were used and in 42% of cases in which stainless-steel screws were used. The corresponding values for multiplanar reconstructions were 92% for cases in which titanium screws were used and 67% for cases in which stainless-steel screws were used. The accuracy of multiplanar reconstructions was statistically better than that of axial images (P < 0.05). Metallic scatter was increased in stainless-steel screws. CONCLUSIONS: The results of this study suggest that the use of computed tomography with multiplanar reconstruction improves accuracy in determining sacroiliac screw position relative to the neuroforamen. The assessment of screw position may be facilitated using titanium screws.

Recurrent rotational deformity of the femur after static locking of intramedullary nails: case reports.

Rotational deformity following intramedullary nailing may cause symptoms and require surgical correction by osteotomy. Reamed, locked intramedullary nailing may be performed, but concern about cortical blood supply and potential pulmonary dysfunction from reaming have led many surgeons to limit this and use smaller diameter nails. Slotted nails are commonly used but are less stiff in torsion than the newer unslotted nails, particularly at the lower diameters. We report two cases of recurrent femoral rotational deformity after using statically interlocked slotted intramedullary nails to correct existing femoral rotational deformities. These patients show that small diameter statically interlocked femoral nails with diminished bone-nail contact must be stiff enough in rotation to avoid potential recurrence.

The cylindrical titanium mesh cage for treatment of a long bone segmental defect: description of a new technique and report of two cases.

This report describes a new technique for treatment of a segmental defect in long bones that uses a cylindrical titanium mesh cage, in combination with cancellous bone allograft and demineralized bone matrix putty (Grafton), stabilized with a statically locked intramedullary nail. Two clinical cases of tibia defects treated with this technique are presented. At the one-year follow-up, radiographically both cases demonstrated excellent limb alignment, stability, and bony healing. Immediate full weight-bearing was initiated in each case, and early limb functional recovery was achieved. Preliminary data suggest that this technique may be a reasonable alternative to currently used methods for management of select long bone segmental defects.

Segmental avascularity of the humeral diaphysis after reamed intramedullary nailing.

Although the clinical experience with reamed intramedullary nailing has been successful for the treatment of femur and tibia fractures, similar success has not been duplicated when this technique has been applied in the humerus. Although the cortical vascular response to nailing of the humerus is presently assumed to be similar to that of the femur, the response of the humerus to reaming has not been documented in vivo. The following case depicts avascularity of the humeral diaphyseal cortex as a complication of reamed intramedullary nailing and illustrates the sensitivity of the humerus to this treatment.

The holding strength of cannulated screws compared with solid core screws in cortical and cancellous bone.

The comparative holding strength of cannulated screws (CS) versus solid core screws (SCS) has not been reported, although differences exist in the respective diameters of their outer thread and pilot drill holes. Our objectives were to characterize these differences and determine the holding power of CS compared with SCS in cortical and cancellous bone. The dimensions of the Synthes (Paoli, PA) 3.5-mm SCS, 3.5-mm CS, 6.5-mm SCS, and 7.0-mm CS were measured, and the cross-sectional area for thread purchase was calculated. Using adult canine femurs, small-fragment 3.5-mm SCS were inserted in cortical (midshaft) and cancellous (condyle) bone of one limb, and CS were placed in similar locations in the contralateral limb. The same technique was used for large-fragment CS and SCS. Pull-out testing was performed using an MTS machine (MTS Systems, Minneapolis, MN) with axial loads applied at 5 mm/s, and data were analyzed to determine the effects of screw type, location, and size. Differences in CS versus SCS design result in higher cross-sectional areas available for SCS thread purchase. Yet no significant differences exists between screw types (SCS vs. CS) in either cortical or cancellous bone. In cancellous bone, large-fragment screws required more force to pull out than did small screws (p = 0.000). The mean force required to pull out small-fragment screws was higher in cortical bone than in cancellous bone (p = 0.000). These data suggest that the clinical decision to use CS versus SCS should not be based on pull-out strength.

The clinician's ability to evaluate the strength of healing fractures from plain radiographs.

The present study was designed to analyze the usefulness of plain radiographs in evaluating bone healing. Rabbit tibiae were osteotomized, externally fixed, and allowed to heal for 3-8 weeks. Bones were harvested, x-rayed, and tested to failure in a dynamic torsion tester. AP and lateral radiographs of 10 rabbit tibia pairs and 10 individual rabbit tibiae were selected randomly for use in a questionnaire, given to 93 physicians who routinely assess fracture healing to evaluate clinicians' ability to assess bone strength. The results indicated that clinicians can differentiate the relative strength of bones by comparing two sets of radiographs. However, the strength determination from a single set of radiographs of a fracture is unreliable, the tendency being to evaluate the fracture to be weaker than it actually is.

Effects of retained diaphyseal plates on forearm bone density and grip strength.

Numerous complications have been attributed to elective plate removal following successful treatment of both bone diaphyseal forearm fractures, yet the effects of retained implants are not known. Fourteen patients were reviewed for residual forearm grip strength (FGS) and bone mineral density (BMD) following uneventful union. Patients were analyzed in two groups based upon time from fixation: group I, > 2 years but < or = 5 years, and group II, > 5 years. In group I, mean 2.6 years follow-up (n = 6), mean FGS ratios (patient values/age matched general population means) were 0.65 and 0.77, respectively, for plated and normal limbs (p = 0.08). The mean BMD ratios of plated/normal sides adjacent to the plate were 0.99 (ulna) and 1.02 (radius); these values were not significantly different from more proximal forearm BMD ratios (p = 0.92 ulna; p = 0.44, radius). In group II, mean 8.4 years (n = 8), mean FGS ratios were 0.97 and 1.09, respectively, for plated and normal limbs (p > 0.05). The BMD ratio was 1.04 adjacent to the plate; this was not significantly different from the ratios measured away from the plate (p > 0.4). We conclude that retained forearm plates can be well tolerated and that their routine removal is not indicated based on FGS or BMD.